Weakly coupled $s = 1/2$ quantum spin singlets in Ba$_{3}$Cr$_{2}$O$_{8}$

TL;DR

This study investigates the magnetic interactions in Ba$_3$Cr$_2$O$_8$, revealing three singlet-to-triplet excitation modes caused by anisotropic interdimer interactions, establishing it as a model for weakly-coupled $s=1/2$ quantum spin dimers.

Contribution

The paper provides a detailed characterization of magnetic interactions in Ba$_3$Cr$_2$O$_8$, highlighting the role of anisotropic interdimer interactions induced by local distortions, and establishing it as a model system for weakly-coupled quantum spin dimers.

Findings

Identified three singlet-to-triplet excitation modes in Ba$_3$Cr$_2$O$_8$

Determined strong intradimer coupling $J_0 = 2.38$ meV

Found weak interdimer interactions $|J_{inter}| \\leq 0.52$ meV

Abstract

Using single crystal inelastic neutron scattering with and without application of an external magnetic field and powder neutron diffraction, we have characterized magnetic interactions in Ba$_3$Cr$_2$O$_8$. Even without field, we found that there exist three singlet-to-triplet excitation modes in $(h,h,l)$ scattering plane. Our complete analysis shows that the three modes are due to spatially anisotropic interdimer interactions that are induced by local distortions of the tetrahedron of oxygens surrounding the Jahn-Teller active Cr$^{5+} (3d^1)$. The strong intradimer coupling of $J_0 = 2.38(2)$ meV and weak interdimer interactions ($|J_{\rm inter}| \leq 0.52(2)$ meV) makes Ba$_3$Cr$_2$O$_8$ a good model system for weakly-coupled $s = 1/2$ quantum spin dimers.